Oxidation of Ultra-High Temperature HfB2–SiC Ceramic Materials in Humid Air Flow

Abstract

The effect of air humidity on the oxidation stability of the ultra-high temperature ceramics HfB₂–30 vol % SiC manufactured by reactive hot pressing technique, was studied by thermal analysis. In the air flow with 100% humidity at 23°C (where the water content was ~3 vol %), the weight gain due to HfB₂ oxidation started at lower temperatures, as well as the weight loss resulting from boron oxide evaporation at temperatures above 1140°C, too. Optical and scanning electron microscopy with local microanalysis confirmed the observation that much less borosilicate glass appeared on the surface and a significantly different microstructure was in the presence of 3 vol % water in air flow.